Carburized drill bit bearing



Sept. 27, 1966 w. J. NEILSON ETAL 3,

CARBURIZED DRILL BIT BEARING Filed Dec. 9, 1963 M4 Z MMJ A/f/d 50/1/ Jay/VF r7566??? INVENTORS United States Patent Ofi 3,275,389 Patented Sept. 27, 1966 ice 3,275,389 CARBURIZED DRILL BIT BEARING William J. Neilson, Whittier, and John F. Fischer, Garden Grove, Calif., assignors to Smith Industries International, Inc., Compton, Calif., a corporation of Cahfornia Filed Dec. 9, 1963, Ser. No. 329,137 2 Claims. (Cl. 308-8.2)

This invention relates to a method of carburizing steel articles with selective deep and thin cases on the same parts and to the resulting product.

Explanatory of the present invention, it has heretofore been quite common to case carburize steel articles. In these methods as heretofore employed the steel parts are heated to a suitable carburizing temperature, usually between 1600 F. and 2000 F. in the presence of a carbonrich atmosphere or a carbon-rich compound. The exposed surfiace of the steel article absorbs carbon therefrom and becomes in effect a case of relatively high carbon steel. Descriptions of carburizing methods may be found in the Metals Handbook, 1948 edition, published by the American Society for Metals, and in other published literature. Methods for selective carburizing, that is, preventing carburization of certain areas of steel articles while carburizing others, are also described in the Metals Handbook. These methods include copper plating, painting with commercial carburization-preventing paints, machining off the case in certain areas, .and other methods.

In all carburization processes heretofore developed the depth of carburization is the same or is uniform in all of the areas of the steel article that are subjected to carburizaation. This often requires a compromise case depth because if certain areas are deep carburized to the depth desired to resist excessive wear other areas may become excessively brittle. Consequently to avoid certain areas becoming excessively brittle those areas which are subject to extreme wear are not carburized to as great a depth as may be desired. This may be particularly true in such articles as the journals on the lower ends of legs of roller well drilling bits. Usually such journals have at least one roller race adapted to receive the rollers of a radial bearing. They also have 'at least one ball race usually functioning as a thrust bearing andthese two races are separated or defined from each other by a rel tively narrow flange; The greatest load on the journal is imposed on the lower half or the lower third of the roller race and consequently this portion of the journal should be carburized with 'a deep However, if the entire roller race andthe entire ball race and the intervening flange are all subjected to deep case carburization the intervening flange becomes excessively brittle and is apt to break ofl resulting in a premature destruction of the bit. By means of the present invention that portion of the roller race which is subject to the most extreme wear can be carburized with a deep case but other portions, such as the ball race and the intervening flange, are only carburized with a relatively thin or shallow case so that the flange will retain the toughness of the base metal and resist break-age. Still other portions on or adjacent the journal are not carburized at all and retain 'fully the toughness of the base metal so that they will not readily break oil. in the course of well drilling.

When the selected areas are subjected to a deep case these areas may be excessively carburized so that their surfaces are excessively brittle. It is therefore 'a further object of the invention to provide a method wherein those areas which are subjected to deep carburization will not be excessively carburized and consequently be excessively brittle.

With the foregoing and other objects in view, which will be made manifest in the following detailed description and specifically pointed out in the appended claims, reference is had to the accompanying drawings for an illustrative embodiment of the invention, wherein:

FIGURE 1 is a vertical section through the lower portion of the leg of a well drilling bit and through its attached journal illustrating the journal as having been carburized in accordance with the present invention.

FIG. 2 is a similar sectional View through the leg and journal illustrating the manner in which the first step of the improved method is performed.

FIG. 3 is a sectional view taken substantially upon the line 3-3 upon FIG. 2 in the direction indicated.

FIG. 4 is a view similar'to FIG. 2 but illustrating the manner in which the second step of the improved can burizirug method is performed.

FIG. 5 is a sectional view through a gear tooth to illustrate another steel article that can be advantageously treated in accordance with the present method.

Referring to the accompanying drawings wherein similar reference characters designate similar parts throughout, 10 indicates the lower portion of a leg of a roller well drilling bit on the lower end of which is formed a journal 11 the axis of which is usually downwardly and inwardly inclined land which serves to rotatably mount a roller cutter C. Usually the journal has formed thereon at least one race for a roller bearing the rollers of which are indicated at 12. Also the journal usually has formed thereon at least one race for a ball bearing the balls of which are indicated at 13. In the course of assembly of the cutter C with the journal the rollers 12 are positioned in their race and the cutter is slipped onto the journal 11 to retain the rollers in place. Thereafter the balls 13 are fed into their race through a ball hole 14 that is subsequently plugged with a ball plug 15 that is welded in place such as indicated at 16.

The reference to the journal of a roller rock bit herein made is largely for purposes of illustration of an important field of application of the present invention but it will be readily understood that the invention is 'not necessarily restricted thereto. As the greatest load that is imposed on the journal occurs on the lower third or lower half of the race for the roller hearing it is desired that this portion of the race be carburized with a relatively deep case. However, if the desired deep case is applied to the race for the roller bearing and also to the race for the ball bearing the intervening or separating flange 17 will be excessively carburized and will consequently become excessively brittle and apt to break. Consequently, although it is desired that the lower portion of the roller race be deeply carburized, a deep carburization of the ball race 13 is frequently unnecessary and a preservation of the toughness of the flange 17 is highly desirable.

In accordance with the present invention, after the leg 10 and journal 11 have been formed of a carburizable steel usually having a carbon content of approximately 20 points, the entire lower portion of the leg 10 and the journal 11, except the lower portion of the roller race, are coated with one or more coats of a coating 18 which will prevent or inhibit carburization as illustrated in FIGS. 2 and 3. Such a coating may be copper plating or in accordance with any of the conventional methodsp The carburizing continues for the maximum number of hours that is economically feasible. The depth of carburization for any given or selected steel is ordinarily a function of time and temperature as expressed in the formula D=X(T) +B in which D equals depth in inches, X equals the constant for any given carburizing temperature, T equals time in hours, and B equals the constant in inches for a given carburizing atmosphere.

In the case of a rock bit journal we normally carburize for thirty hours or longer at 1700 F. to obtain a case on the lower half of the journal .150" deep or deeper.

As a means for creating a carbon-rich atmosphere about the journal during the carburizing we employ isopropyl alcohol which is allowed to drip regularly into the heating furnace. The products obtained from the cracking of the alcohol are continuously circulated through the furnace by means of a power-driven fan. After the journal has been thus subjected to the carbon-rich atmosphere for approximately one-half of thetotal time the introduction of the isopropyl alcohol is discontinued so that the atmosphere thereafter. for the remainder of the thirty hours is approximately neutral. During this latter portion of the thirty-hour period some diffusion of the absorbed carbon takes place so that the carbon content on the exposed surface of the journal does not remainexcessively high.

When the first step of carburizing is completed the journal should be thoroughly cleaned to removed soot and the protective coating and to conditionthe surface for further carburizing. We usually sandblast all sur- Thereafter certain surfaces are left exposed and other surfaces are again protected from carburization faces.

such as by copper plating or by the application of one or more coats of a paint which will prevent or inhibit carburization. Thus, as illustrated in FIG. 4, the lower half of the roller race is left exposed, the surfaces of the ball race may be left exposed and even the surfaces. of the intervening flange 17 may be left exposed. The exterior surface of the leg may be coated with the coating as indicated at 19 and this coating may extend around the thin fin 20 thatis left at the bottom of the leg 10 below the journal 11.; Also selected areas may be coated with the coating as indicated at 21 and 22. The journal is then subjected to a econd carburization. During this second carburization the ball race, the intervening flange 17 and exposed areas on'the leg 10 surrounding the base of the journal are given a relatively thin case. That portion of the roller race that was initially exposed is, of course, also subjected. to additional carburizing. This causes the deep case areas on the lower half of the roller race to deepen slightly and produces the thin case on the areas where a thin case isdesired. As the flange 17 will only have a thin case it will retain much of the initial toughness of the base metal and consequently resist breakage during usage.

During the second carburizing step the leg and journal are heated to approximately 1700 F. for a much shorter time to obtain the thin case and, as in the first step,

during the latter portion of the period the supply of isopropyl alcohol is discontinued to permit some carbon diffusion to take place so that the carbon content ofthe exposed surfaces is not excessively high.

On'the completion of the second carburization theleg is cooled to approximately 1550 F. and then quenched in oil although other quenches may be em- The leg and journal may thereafter be heated to approximately 1475 F.,

ployed where deemed desirable.

quenched in oil and tempered or drawn at approximately 425 F. to produce :the desired case hardening. Other conventional steps of case hardening the structure may be employed after the construction of the second 1' carburizing step..

Where the carburizing steps are performed employing carbon-rich compounds instead of carbon-rich atmospheres it may be necessary to remove or withdraw some ofthe excessive carbon near the surface that is absorbed by the steel during each of the carburizing steps. Thus endof each carburizing step .to a neutral atmosphere or even to an oxidizing atmosphere.

In FIG. 5 we have illustrated another application of the present invention to a steel article such as a gear tooth. In the usual gear tooth the sides of the tooth are subjected to a combined rolling and sliding action and are consequently subject to the greatest abrasive Wear. These sides should consequently be protected with a relatively deeplcase. of the gear tooth that are near its base should not be excessively carburized or rendered excessively brittle. Otherwise the gear tooth may break off across the base.

In accordance with the present. invention areas of the sides. of the gear tooth, indicated at. 23, are left exposed but other. areas such as those indicated at 24 may be protected from carburizing by preventing or inhibiting The areas 23 are then subjected to carburizing under conditions that will produce a relatively deep coatings.

case and when this is completed the coating is removed from the areas 24 and the gear again subjected to car-:

burizing under conditions that will produce a relatively thin case. Areas 25:may be coated during the .second carburization.

From the above described method it will be appreciated that we have developed a new-process of carburization and the resulting article wherein only a portion of the steel article has its exterior surface exposed to the first carburization to produce a relatively deep case. Thereafter other areas as well as the mentioned portion are subjected to carburization under conditions that will produce a relatively thin case. Those portions of the article that are subject to extreme wear will consequentlybe adequately protected and thoseportions which are.

not subject to such extremewear will not only be adequately protected but will have theirequisite toughness retained to resist breakage. thin such as the fin 20 and are not subject to, any great amount of abrasive wear vbut because of their structure must be of maximum toughness, these areas can be protected during both carburization steps so that they will not be carburized to any extent whatsoever.1

The invention is applicable tor-any carburizable steel including not only those steels which contain normal 1 or usual impurities but alsothose steels which, may be regarded as low alloy steels containing small amounts of nickel, chromium, cobalt and the like.

Various changes may-be made in the details of the steps of the process without departing from rthespirit and scope of the invention asdefined by the appended claims.

We claim:

1. A journal for a well drilling bit having a roller 1 race .and a ball race separated by a flange wherein'the. lower portion of the roller race is deep carburized and q the upper portion of the roller-race, the entire ball race, and the flange are thinly carburized.

However those portions Where certain portions are thinly carburized, and the is free of carburization.

5 fin at the bottom of the leg References Cited by the Examiner UNITED STATES PATENTS Cooper.

Schlumpf et a1. 3088.2 Fermier 175370 X Brown 175--370 X 6 Latzen 308241 X Engelhard 14816.5 Ahrens 148-16.5 Goodwin 308-8.2 Peter 308-8" DAVID J. WILLIAMOWSKY, Primary Examiner. L. L. JOHNSON, Assistant Examiner. 

1. A JOURNAL FOR A WELL DRILLING BIT HAVING A ROLLER RACE AND A BALL RACE SEPARATED BY A FLANGE WHEREIN THE LOWER PORTION OF THE ROLLER RACE IS DEEP CARBURIZED AND THE UPPER PORTION OF THE ROLLER RACE, THE ENTIRE BALL RACE, AND THE FLANGE ARE THINLY CABURIZED. 